Iwas introduced to Baudelaire on my 14th birthday, when my parents gave me a bilingual edition of Les Fleurs du mal translated by Richard Howard, a black volume with devilish-looking white and purple lilies on the cover. That evening I read the entire collection in a trance, sucked into its splendid savagery and brutal humanity, its febrile voyages and sharp, bracing portraits of urban solitude. And then there was all that spleen, a dark river of malaise coursing through nearly every landscape, inner and outer.

Impatiently, I searched for more, and soon discovered the prose poems: 50 vignettes, for the most part urban, of astonishing power. Le Spleen de Paris or Petits Poèmes en prose was written during the last 12 or so years of Baudelaire's life. They represent a distillation and intensification of earlier themes, moralistic tales that often end with a sardonic flourish.

What greater genre than the prose poem, that magical space between poetic stillness and the slightly higher frequency of prose? In Baudelaire's hands it is painterly, photographic, a thought unfurled into half a page, one or three. A capricious moon spills her light onto a sleeper's face, casting an ambiguous spell. A rich boy stares longingly through the gates of his castle at a young pauper playing with a pet rat. An ageing acrobat, a portrait of the poet in his twilight, sits hunched in the wings. Beauty unveils her cruel, callous gaze. Most of the poems depict a dramatic encounter (or quieter overlap) between two realities, often triggering an existential crisis in the weaker party while the stronger carry on, untouched.

Baudelaire reminds the reader that on the flip side of beauty lies some form of monstrosity. Each poem seems to echo: never let down your guard. Even the finest and deepest of reveries will, at some point, be cut short by a crude knock at the door.

He also set the model for urban alienation, that familiar solitude within a crowd. Looking back, it was Baudelaire who probably first inspired me to search, in every city, for the marginal and strange, to focus on what's on the pavement's periphery rather than at its centre.

And how familiar, the impulse to withdraw from "the tyranny of the human face" yet, once alone, how easy to turn on oneself. Throughout my adolescence Baudelaire's photograph hung to the right of my bed, a brooding portrait taken by Etienne Carjat in around 1863, during the final years of the poet's life. It sits in my study today, always behind me as I write, penetrating, astute and defiant.